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Solution: The differences between storage devices of AR series routers are described as follows:
AR1200 series routers: Support flash memory and USB flash disks. Flash memory is embedded in the device by default. Users can extend the device storage with two USB flash disks.
AR2200 series routers: Support flash memory, USB flash disks, and Micro SD cards. Flash memory and a Micro SD card are embedded on AR2220 and AR2240 by default. Flash memory is embedded on AR2201-48FE, AR2202-48FE, AR2204, and AR2220L. Users can extend the device storage with two USB flash disks and a Micro SD card.
AR3200 series routers: Support flash memory, USB flash disks, and Micro SD cards. Flash memory and a Micro SD card are embedded in the device by default. Users can extend the device storage with two USB flash disks and a Micro SD card.
For details, see the following URL: What Storage Devices Do AR Series Routers Support?

The difference between NAT Server and NAT Static configuration is: NAT Server to access the Internet from intranet, only do address replace, but NAT Static for network address; active access outside the network will also replace the address and port number.